Magnetoplasmadynamic apparatus for the separation and deposition of materials

ABSTRACT

A plasma arc discharge method for deposition of metallic and semiconductor layers on a substrate for the purpose of producing semiconductor grade materials such as silicon at a reduced cost. Magnetic fields are used so that silicon ions and electrons can be directed toward a target area where they are deposited. The ions and electrons are preferably injected as a compound in gaseous of liquid form but may also be injected in liquid elemental form or vaporized from a thermionic cathode. The magnetic fields include an accelerating magnetic field and a focusing magnetic field. The accelerating magnetic field is adjusted to support a desired high ion flux rate and the focusing magnet can control the plasma beam direction and divergence. 
     The silicon provided in a compound form or in the form of metallurigical silicon is purified during the deposition process by a carrier substance which may be a part of the compound or separately injected. Chemical purification is accomplished by separation of the silicon due to ionization potential differences between silicon and other elements. The magnetic acceleration technique allows the use of pressures under 10 -1  torr thereby facilitating plasma formation and allowing the materials to be deposited with a desired high purity.

This is a continuation of application Ser. No. 210,240, filed Nov. 25,1980, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The separation of materials can be accomplished by the application orthe influencing of forces on intrinsic species of the material or onspecies of a compound of materials. These forces can be gravitational,electromagnetic, chemical, gas (fluid) dynamic and/or a combination ofthese forces. The forces will provide different acceleration to thespecies thereby giving different spatial and temporal characteristics tothe desired separation. The material could be in the solid, liquid,vapor or plasma state, or a combination of these states. Themagnetoplasmadynamic process encompasses each or a combination of thesestates.

The magnetoplasmadynamic phenomena was first discovered in 1961 by Cannand described in U.S. Pat. No. 3,243,954. A device that was designed andtested was intended for space propulsion applications and is commonlyknown as an ion propulsion system. The principal design and performancerequirements were to fully ionize a single species vapor and accelerateall the ions to a preferred high velocity into space. The device was tohave high thrust efficiency, where thrustor efficiency was defined as

Thrust efficiency=.sup.η mass·.sup.η exhaust·.sup.η power where ##EQU1##Thrust Power=m_(ions) ×(ν)²

where

    m.sub.ions=mass flow of ions

    ν=average velocity of ions

No attempt was made to separate materials in this process as theintended application did not direct the development to that end.

The magnetoplasmadynamic phenomena is simply the controlled interactionof a plasma and an applied magnetic field through the induced magneticfield resulting when the plasma is accelerated by an appliedelectrostatic field (potential). This type of interaction phenomena isreferred to as the Hall Current effect. The significance of the work ofCann and others was the controlled feed or propellant injection into thecavity anode region. The proper voltage selection and propellantinjection rate resulted in ionization and acceleration of the chargedparticles (ions and electrons) in the direction parallel to the appliedmagnetic field. The resulting plasma was accelerated to the desiredexhaust velocity.

This invention relates to the separation of materials by new andimproved methods employing magnetoplasmadynamics. The invention allowsthe separation and collection of materials that cannot be separated byother techniques or processes. The invention also separates materialsthat can be separated by other techniques or processes but thisinvention would separate the material at lower costs.

An important use of methods and apparatus of this invention is theproduction of semiconductor grade silicon from low-cost siliconcompounds as the feed material. Semiconductor grade silicon isconsidered to be silicon which is made at least 99.9999% pure byrefining techniques. For efficient operation of silicon solar cells thesemiconductor grade silicon should actually be at least 99.999% pure andpreferably 99.9999% pure. On the other hand, silicon which is at least97% pure is considered to be metallurgical grade silicon. Commerciallyavailable metallurgical grade silicon is approximately 98% pure. Thecost of semiconductor grade silicon is significantly greater than thatof metallurgical grade silicon. In 1980, semiconductor grade siliconcost approximately $80./Kg, whereas metallurgical grade silicon costless than $1.00/Kg.

Ironically, the semiconductor grade is valued because it is usually usedin products which require that specified impurities or "dopants" beadded to the silicon. These dopants affect conductivity of the siliconand create donor and receptor portions on semiconductor devices.Therefore, as used in this specification, "semiconductor grade silicon"should be construed to include the highly pure silicon which has dopantsadded.

As noted, the semiconductor grade silicon is used to produce diverssemiconductor devices, including silicon solar cells. It is essentialthat the cost of solar cell production be reduced so that the cost ofproduction of solar cells be recovered over the expected lifetime of thesolar cells. At the present time silicon solar cells are made fromsingle crystals of n-type silicon about 4 centimeters in diameter and aslong as a sausage. These crystals are made by rotating and pulling at aslow regulated pace. The elongated crystal is then cut into slicesapproximately 50 microns thick by means of a diamond-tipped circularsaw. After the slices are ground, lapped and chemically cleaned, theyare placed in a diffusion chamber which consists of a long quartz tuberunning through a cylindrical electric furnace. In the diffusionchamber, the crystals are heated to 1150° in an atmosphere of borontrichloride. Elemental boron, which decomposes from the boron compound,diffuses into the outer surfaces of the silicon wafers, thus doping thewafers to create a p-type layer less than 0.3 microns thick. Furtherprocessing is necessary to create the terminals and to expose the n-typesilicon, now sandwiched in the middle.

While this process may be ideal for the production of small electroniccomponents, the steps involved put the price of solar cell panels atover $12,000.00 or (1973 dollars) per kilowatt of generated power. Whilethe real cost of production is expected to decrease in accordance withthe refinement of production techniques and mass production, the priceis still several orders of magnitude too large for solar panels to beused commercially for power production in other than remote areas suchas space ships. Also, in many cases the energy spent in productioncannot be recovered over the expected lifetime of the solar cells.

Several systems have been proposed for the production of semiconductordevices, such as solar cells, by other means. For example, Janowiecki,et al., U.S. Pat. No. 4,003,770 (also United States Patent OfficeVoluntary Protest Program Document No. B 65105) discloses a process forpreparing solar cells in which p- or n- doped silicon particles areinjected into a plasma stream where the particles are vaporized. Theheated particles are then discharged from the plasma stream onto asubstrate to provide a polycrystalline silicon film. During the heatingand spraying, a suitable atmosphere is provided so that the particlesare surrounded to inhibit oxidation. However, Janowiecki, et al. do notsuggest the use of his techniques for refining the silicon. Walter H.Brattain in U.S. Pat. No. 2,537,255, discloses the deposition of siliconfor silicon photo-emf cells, using a mixture of hydrogen and silicontetrachloride. However, this early technique does not disclose the useof a magnetoplasmadynamic effect for either production of these solarcells, nor the refining of metallurgical grade silicon intosemiconductor grade silicon.

Tsuchimoto in U.S. Pat. No. 3,916,034 discloses a method fortransporting semiconductors in a plasma stream onto a substrate. Theplasma is directed by magnetic fields onto thin film substrates.Tsuchimoto is typical of conventional ionization chambers for use with amagnetogasdynamic process. In that magnetogasdynamic process, massutilization efficiency is low, making the method ineffective forrefining mass quantities of silicon.

It is also possible to provide a deposition system using amagnetoplasmadynamic arc in which a magnetic nozzle is produced by amagnetic coil and/or the self-magnetic field of discharge. This magneticnozzle permits a higher ion density in plasma jet, giving better controlover the distribution of silicon in the jet. The anode attachment can bediffused or made to rotate rapidly during the electromagnetic (j×B)forces, permitting uniform erosion of the anode. However, this systemprovides a "modal" performance, in that small changes in the mass flowrate critically affect the voltage requirements of the system. In thissystem, an insulator between the anode and cathode is subject to erosionor may short out the discharge by being coated during the operation ofthe plasma device.

SUMMARY OF THE INVENTION

It is accordingly an object to provide a method and apparatus forrefining silicon, and particularly for refining metallurgical gradesilicon into a purer form of silicon to produce semiconductor gradesilicon.

It is a further object to produce semiconductor grade in thin filmshaving large areas, thereby providing an inexpensive base product formaking silicon photovoltaic solarcells.

It is a further object of this invention to provide a method of refiningmaterials such as silicon in layers using magnetoplasmadynamictechniques.

Accordingly, it is a further object of the present invention to providea new and improved method and apparatus for the separation of materialswhich does not depend upon conventional chemical reduction processes,conventional catalytic processes, vapor transport processes, laserheating, differential ionization, electron beam heating or a meltedcrystal pull process to obtain separation of species. However, a furtherobject of the invention is to provide a new and improved means ofelectromagnetic separation by selective ionization and acceleration in amagnetic field. Particularly it is an object to provide a method andapparatus which has a low cost relative to present separators and whichrequires less power to operate.

It is a further object of the present invention to provide a means toform large area silicon films used for solar cells, and particularlylarge area silicon solar cells in a process which is economical tooperate and which has a low power consumption.

It is still a further object to refine silicon for solar cells to beused in terrestrial applications in which the cost of production of thesolar cells, and particularly the power consumption costs of production,are significantly less than the value of the power expected to beproduced by the solar cells during the lifetime of the solar cells.

Accordingly, the invention, in one aspect thereof, is directed to anapparatus for depositing materials in layers to form semiconductivedevices by means of electrodeposition. A plasma spray is magneticallyaccelerated in a vacuum chamber by means of a magnetoplasmadynamicgenerator comprising a cathode, a anode an accelerating magnet adjacentto the cathode and a focusing magnet. The focusing magnet has a fluxpattern which can be rotated so as to direct the plasma spray indifferent directions as the plasma spray is ejected from the plasmagenerator. In one aspect of the invention, a means is provided forinjecting materials into the plasma in order to create a plasma stream.These injected materials may comprise a carrier used for separatingundesired impurities from the silicon in the plasma spray. The injectedmaterials may also comprise dopants used for depositing a doped layer ofthe semiconductor. The doped layer can be of any desired thickness.

In another aspect, the focusing magnet may be placed on a gimball so asto allow the magnetic flux field of the focusing magnet to be rotated,thereby permitting deposition of materials evenly on various portions ofthe target area.

In yet a further aspect of the invention, the apparatus is used todeposit a substrate before the semiconductor material is deposited.

In still another aspect, this invention is directed to a method forproducing semiconductor materials such as semiconductor grade silicon ina vacuum environment. A plasma is established between a cathode and ananode. The plasma is accelerated with an accelerating magnet and focusedonto a deposition area located on a target area with a focusing magnet.The semiconductor material, such as silicon, is placed in the plasma,thereby forming the plasma stream, and a carrier substance is injectedinto the plasma stream in order to purify the semiconductor materialwhile it is in the plasma.

The deposition area may be moved along the target area by changing theflux orientation of the focusing magnet.

In yet another aspect, the completed semiconductor films may be removedfrom the target area by a robot means so that subsequent semiconductorfilms may be formed without the requirement that the vacuum chamber bepumped down each time a new semiconductor film is to be formed.

In yet another aspect, this invention is directed to a method forrefining materials such as semiconductor grade silicon and particularlyto the refining of silicon in which a vacuum environment is provided anda plasma is accelerated with an accelerating magnet and focused onto atarget area with a focusing magnet. The material to be refined is placedin the plasma, thereby forming a plasma stream. A carrier substancecombines with impurities in the materials to be refined. Therefore, thematerial is deposited onto the target area while impurities found in thematerial are removed with the substance primarily as a compound with thecarrier by means of a vacuum pumping apparatus. By adding appropriatematerials, such as dopants, the refined material can be modified in theplasma stream as the material is being deposited on the target area.

This invention also provides a means for preferential isotopeseparation. Separation of most compounds can also be effected forpurification, etc.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of the magnetoplasmadynamic deviceaccording to the invention.

FIG. 2 is a schematic representation of the arc-forming section of apreferred embodiment of the invention.

FIG. 3 is a block diagram representing the process of formingsemiconductor films in accordance with this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, the magnetoplasmadynamic deposition device 1according to the invention is contained within a vacuum housing 11. Inan upper portion 13 of the magnetoplasmadynamic device 1, is anarc-forming section 15 surrounded by an accelerating magnet 17 and thelower portion of the magnetoplasmadynamic deposition device 1 forms adeposition chamber 19. A center portion 21 of the device 1 is surroundedby a focusing magnet 23, with the deposition chamber 19 located directlybelow the arc in the arc-forming section 15 may be accelerated downwardby the accelerating magnet 17. The focusing magnet 23 tends to maintainthe plasma within a narrow column, designated by reference 25, until theplasma reach the deposition chamber 19.

In order that some of the ions in the column 25 may be projected intothe deposition chamber 19, it is necessary that a vacuum be maintainedwithin the vacuum housing 11 so that the ions within the plasma column25 are not obstructed by other fluid material between the arc-formingsection 15 and the deposition chamber 19. In the preferred embodiments,a very high vacuum is maintained so that the pressure is below 10⁻⁴Torr. It is preferred that a vacuum of 10⁻¹⁰ Torr be maintained,although this may prove uneconomical, particularly if substantialamounts of carrier materials are used. In order to accomplish these highvacuums, a combination of cyrogenic and ionic pumping is used, usingconventional cyrogenic and ionic pumps (not shown).

Additional extraction of carrier materials is accomplished by a liquidnitrogen-cooled coil assembly 31. The coil assembly 31 is located in thecenter portion 21 so as to surround the column of plasma 25. Gases whichescape from the plasma within the column 25 then condense on the coilassembly 31.

As shown in FIG. 2, the arc-forming section 15 comprises a rod-likecathode 41 and a cylindrical anode 43. An injector 45 is mountedadjacent the cathode so as to permit injected fluid to pass over thecathode 41. When an arc is established between the cathode 41 and anode43, fluid in the vicinity of the arc is ionized, thus forming an ionizedplasma stream.

Referring back to FIG. 1, the fluid ionized in the arc-forming section15 is accelerated by the accelerating magnet 17 and focused by thefocusing magnet 23 in order to form the narrow column of plasma 25.However, if the fluid injected by the injector 45 is composed of orforms elements and compounds of differing ionization potentials, theelements or compounds with the highest ionization potentials will bemore affected by the magnetic forces and will therefore tend to displacethose elements or compounds with a lower ionization potential within thecolumn of plasma 25. Furthermore, if binary, rather than ionic compoundsare formed, these compounds will tend to very rapidly separatethemselves from the plasma stream. Thus, such binary compounds may berapidly extracted. In other words, the ions formed by injecting fluidwith the injector 45 are under the influence of the electromagneticfields formed by the accelerating and focusing magnets 17, 23, andfollow restricted trajectories. Those atoms which are not under theinfluence of the electromagnetic field are free to diffuse out of theplasma stream. The different trajectories provide a means for separatingmaterial species.

Because of the different ionization potentials of different materials,the materials can also be separated by ionizing all of the materials.The resulting ions will have different masses and ionization potentialsand will, therefore, have different trajectories as they come under theinfluence of the electromagnetic fields of the accelerating and focusingmagnets 17, 23.

As will be described later, in the preferred embodiment, silicontetrachloride will be the primary material injected through the injector45. Elemental silicon becomes separated from the compound in thearc-forming section, thereby leaving chlorine and impurity-containingchlorides. The device must now incorporate some technique of separatingthe chlorine from the silicon while still insuring that the partialpressure (of chlorine) within the vacuum housing 11 remains adequatelylow (less than 10⁻⁴ Torr). Because of the difference in the ionizationpotential between silicon and chlorine, the arc will preferentiallyionize the silicon. The silicon ions will be trapped by the appliedmagnetic fields and the chlorine will diffuse out of the narrow columnof ions 25. The coil assembly 31 constitutes the primary element in acyrogenic pumping tower. Between the column of ions 25 and the coilsassembly 31 are baffles 51 which serve to protect the coil assembly 31and to prevent the coil assembly 31 from disturbing the narrow beam ofplasma.

When the narrow beam of plasma 25 enters the deposition chamber, ionsremaining the narrow beam of ions deposit upon a target 53, thus forminga layer or a semiconductor device. Since it is desired that ultimatelythe semiconductor materials be used outside the device 1, thesemiconductor materials, such as the silicon should be removable fromthe target area. There are several methods of accomplishing this:

1. A semi-permanent or temporary layer of a material to which thesilicon does not adhere may be placed over the target area. An exampleof this type of material would be boron nitrite. Depending upon theinterface temperature, the boron nitrite will decompose to some extentand the boron will diffuse into the silicon film deposited on the boronnitrite. This results in heavy doping which renders the bottom surfaceof the silicon conducting (approximately=10⁻³ ohms/cm). This permits thebottom surface to act as a back conductor for a semi-conductor devicewhich will be formed from the semiconductor material.

2. The silicon can be deposited on a reusable substrate sheet of arefractory material such as molybdenum or tungsten. By properlycontrolling the thermal cycling of the substrate, the silicon depositedthereon can be made to break loose from the refractory sheet due to thedifference in the thermal expansion coefficients of the two materials.

3. The silicon can be deposited on the surface of a "lake" of highdensity, low vapor pressure liquid metal such as tin.

Where the silicon is deposited on solid material (as in cases 1 and 2),it may be desirable to scribe the target materials with grooves in orderto facilitate directional growth of metallic crystals which aredeposited on the target materials. These grooves could be 5-19 micronsdeep, 5-10 microns wide and have a center-to-center separation of 10-15microns between adjacent grooves. This will encourage crystallinenucleation centers formed during the deposition of the silicon to align,thereby producing large crystals or even a single crystalline film.

Dopant Injection

It is possible to inject a dopant material into the plasma stream inorder to provide a doped layer on the semiconductor material whilecontrolling the depth and density of the doped layer. This is done byinjecting a dopant simultaneously with the primary semiconductormaterial, either in the same injection port or separately. Thus, as thesemiconductor ions are deposited, the dopant, which is placed in thenarrow column of plasma 25, diffuses into the silicon when the siliconis deposited onto a target 53.

Also, as mentioned before, when silicon is deposited on a sheet of boronnitrite, boron doping of the silicon will occur, especially near theinterface between the silicon and the boron nitrite. The temperatures ofthe substrate and of the film will determine the concentration andpenetration of the boron into the silicon.

The following table lists the physical properties of the variousmaterials injected by the system. Ideally, the material injected shouldbe in a fluid form. The ionization potential of those elements which areto be deposited should be relatively high and the ionization potentialof carrier materials should be relatively low. The melting and boilingpoints of the materials are important for the purposes of extracting thematerials by passing cryogenic materials through the coil assembly 31.

    __________________________________________________________________________                          Chloride         Vapor                    Ionization                          and/or           Pressure (Torr)    Symbol         Material               Mol. Wt.                    Potential                          Hydride                               M.P. °C.                                     B.P. °C.                                           195.8 °C.    __________________________________________________________________________    Si   Silicon               28.06                     8.12 (M.P. Si = 1420° C.)    Cl   Chlorine               35.46                    12.95 Cl.sub.2                               -101.6                                     -34.7 10.sup.-9    H    Hydrogen                1.00                    13.53 H.sub.2                               -259.14                                     -252.8                                           10.sup.3    N    Nitrogen               14.01                    14.48 N.sub.2                               -209.86                                     -195.8                                           760         Hydrogen               36.46                    N.A.  HCl  -112  -83.7 1.5 × 10.sup.-5         Chloride    Preferred Substances    1.   Tetra-               168.29                    N.A.  SiCl.sub.4                               -70   57.57 N.A.         chloro-         silane    2.   Tri-  135.44                    N.A.  SiHCl.sub.3                               -134  33.   N.A.         chloro-         silane    3.   Di-   100.99                    N.A.  SiH.sub.2 Cl.sub.2                               -112  8.3   N.A.         chloro-         silane    4.   Chloro-               66.54                    N.A.  SiH.sub.3 Cl                               -118.1                                     -30.4 N.A.         silane    5.   Silane               32.09                    N.A.  SiH.sub.4                               - 185 -111.8                                           N.A.    6.   Disilane               62.17                    N.A.  Si.sub.2 H.sub.6                               132.5 -14.5 N.A.    7.   Tri-  92.24                    N.A.  Si.sub.3 H.sub.8                               -177.4                                     52.9  N.A.         silane    8.   Tetra-               122.32                    N.A.  Si.sub.4 H.sub.10                               -93.5 80    N.A.         silane    __________________________________________________________________________

Process Automation Considerations

In order to produce many square meters of semiconductor grade siliconfilm with one vacuum pump-down operation, some method of moving thesubstrate and/or the target material must be devised. In the embodimentin which a solid substrate is used for a target area, solar cell filmswhich are deposited on the target 53 would be removed from the target 53and stored within the vacuum housing 11, thereby allowing subsequentfilms to be deposited at the target 53.

A robot 55 would be used to lift the subsequent films from the target53. A plurality of completed films 57 are then stored by the robot 55 inthe deposition chamber 19 away from the target 55 and the plasma column25. It can be seen that this storage of completed films 56 permits thedevice 1 to continue to deposit subsequent films.

It is also possible to have the robot 55 place preformed substrated (notshown) on the target 53 prior to the deposition of each film by thedevice. Thus the completed films 57 would each have their own substrateswhich may be left with the films or later separated from the films.

In the case where the silicon is deposited on the surface of the liquidmetal, the robot 55 may be used to pull the film along the surface ofthe liquid. The film may be continuously deposited and a cutting meanssuch as a laser (not shown) may be used to sever the film into desiredlengths before the lengths are stored as completed films 57.

Operation

Referring to FIG. 3, the process of refining silicon is achieved bycarefully controlling the different materials that are injected into thesystem, as well as the arc control and plasma focusing parameters.Pressure from a pressure contol 61 is applied to a source of silicontetrachloride 63. The silicon tetrachloride is injected into thearc-forming section 15 by means of a vaporizer and flow controllerapparatus 65. Hydrogen from a hydrogen source 77 may be injected inorder to provide additional carrier gas to remove impurities and tofacilitate the formation of plasma spray. The various gases formed inthe arc-forming section 15 are pumped out at a vacuum pumping section79. The ions emitted from the arc-forming section 15 are preferentiallyionized in order to direct silicon and other materials to be depositedat the target 53 (FIG. 1) in a step represented by block 81. This isachieved by the out-gassing performed by the vacuum pumping section 79,as well as the focusing magnets 23. The focusing magnets direct the ionstoward the target 53 in the deposition chamber 19, as represented bystep 83. In step 85, the substrate is prepared to accept the column ofions 25. This step includes the thermal processing of the substrate inorder to provide the substrate at a proper temperature to either adhereor gradually separate from the deposited materials, as desired. This isrepresented as a part of the processing of the substrate by block 87.The ions, as they impinge upon the target, form a crystalline film,represented by a step 89. The hydrogen provided at 77 may be used toform an plasma beam in order to thermally process the silicon and toprepare the silicon to receive a dopant layer. This is represented byblock 91.

Final processing performed at block 97. This processing may include thedeposition of a thin arsenic layer in order to improve thephotosensitive characteristics of the resultant photocells. Finally, instep 99, after the last silicon films are formed, the completed films 57are removed from the deposition chamber 19.

Articulating Magnets

If it is desired to create large area film substrates, it is necessaryto articulate the target 53 with respect to the narrow column of plasma25. This articulation provides a larger spray pattern on the target 53than would be achieved by merely permitting the column of plasma 25 todiffuse.

As previously mentioned, in the case in which the narrow column ofplasma 25 is focused onto a liquid metal substrate, the robot 55 may beused to pull the deposited materials along the "lake" of liquid metal,thus effectively removing the target 53 relative to the narrow column ofplasma 25.

However, when a solid substrate is used, it is necessary to either movethe target 53 or the column of plasma 25. If it is desired that thetarget 53 be retained in a specific location, then the narrow column ofplasma 25 may be articulated by shifting the magnetic fields of thefocusing magnet 23. This can be achieved by providing an articulatingportion 101 of the focusing magnet 23. The articulating portion 101functions as a part of the focusing magnet 23 but is capable of shiftingits magnetic axis or of shifting its flux pattern in order to angularlydivert the narrow beam of plasma 25 as the plasma approach the target53. This may be done by selectively energizing parts of the articulatingportion 101 or by physically rotating the portion 101 on a gimballapparatus.

While my invention is described in what is believed to be a preferredembodiment, it is anticipated that further modifications will have to bemade in order to increase the efficiency of operation of amagnetoplasmadynamic refining technique. As an example, it is possibleto deposit a plurality of silicon films on the target 53 with removableor disposable substrates deposited between the films in a sandwich-likefashion. This would eliminate the necessity to store the completed filmsaway from the target 53. It is anticipated that other elementalseminconductors, such as germanium, may be used in place of silicon.Accordingly, my invention is described but not limited by thedescription of the preferred embodiment.

I claim:
 1. An apparatus for refining semiconductor materials by using aplasma spray magnetically accelerated in a vacuum comprising:(a) avacuum chamber and associated vacuum pumping apparatus; (b) amagnetoplasmadynamic Hall effect plasma generator, the plasma generatorfurther comprising:a cathode an anode an accelerating magnet locatedadjacent that portion of the cathode closest to the anode; a focusingmagnet at least part of which is located beyond the anode with respectto the cathode; (c) a plasma generator support structure, the supportstructure supporting the plasma generator within the vacuum chamber; (d)a means to supply the plasma generator with electric power, the electricpower being primarily direct current and the power enabling the plasmagenerator to create a plasma; (e) a target surface, the target surfacebeing located beyond the focusing magnet with respect to the cathode andanode; (f) a means for injecting materials into the plasma in order tocreate a plasma stream; (g) an access door enabling access to the insideof the vacuum chamber from the outside, the access door having sealingmeans, whereby said injected materials are preferentially ionized by theplasma generator, thereby causing impurities in the materials toseparate while they are in the plasma stream.
 2. The apparatus of claim1 wherein the means for injecting materials into the plasma is adaptedto receive a carrier material, the carrier material being effective tocombine with impurities in semiconductor materials in the plasma streamin order to separate the impurities from the semiconductor materialbefore the semiconductor material is deposited at the target area, thuspermitting the semiconductor material to be deposited in a state ofpurity which is greater than the purity of the semiconductor materialbefore deposition.
 3. The apparatus of claim 2 wherein the means forinjecting materials into the plasma is further adapted to inject dopantmaterial so that the dopant material may be applied to the semiconductormaterial as the semiconductor material is being applied to the targetarea.
 4. The apparatus of claim 3 wherein the dopant is mixed with thecarrier material.
 5. The apparatus of claim 2 further comprising a robotmeans, the robot means being operable to move materials to and from thetarget area.
 6. The apparatus of claim 5 wherein the cathode is athermionic cathode.
 7. The apparatus of claim 2 wherein elementalsilicon is injected as a liquid into the plasma generator during theoperation of the apparatus.
 8. The apparatus of claims 2 or 3 whereinthe means for injecting materials injects the materials adjacent to thecathode.
 9. The apparatus of claims 1 or 3 wherein the cathode is athermionic cathode.
 10. The apparatus of claims 1 or 2 wherein siliconis injected into the plasma generator during the operation of theapparatus.
 11. The apparatus of claim 10 wherein the silicon is injectedas a fluid compound.
 12. The apparatus of claim 10 wherein the siliconis injected at the anode.
 13. The apparatus of claim 10 wherein thesilicon is injected at the cathode.
 14. The apparatus according to claim1 or 2 wherein the vacuum pumping apparatus comprises a cryogenic vacuumpump and an ion vacuum pump.
 15. The apparatus of claim 1 wherein theinjected materials comprise silicon and the preferential ionization andthe separation of impurities from the semiconductor materials results insemiconductor grade silicon being deposited at the target surface. 16.The apparatus of claims 1 or 15 wherein a coil assembly is provided forcondensing materials which escape from the plasma stream.
 17. Theapparatus of claims 1 or 15 wherein the plasma generator is surroundedby an accelerating magnet which accelerates the plasma thereby causingthe materials in the plasma to be transported away from the plasmagenerator.
 18. An apparatus for refining semiconductor metals used toform semiconductor junction devices by means of a plasma spraymagnetically accelerated in a vacuum comprising:(a) a vacuum chamber andassociated vacuum pumping apparatus: (b) a magnetoplasmadynamic Halleffect plasma generator, the plasma generator further comprising:athermionic cathode; an anode; an accelerating magnet located adjacentthe cathode; a focusing magnet, at least part of which is located beyondthe anode with respect to the cathode; (c) a plasma generator supportstructure, the support structure supporting the plasma generator withinthe vacuum chamber; (d) a means to supply the plasma generator withelectric power, the electric power being primarily direct current andthe electric power enabling the plasma generator to create a plasmastream with ions from the thermionic cathode; (e) a means to supplysemiconductor materials to the plasma generator, the semiconductormaterials having a degree of purity less than that required forsemiconductors; (f) a target area, the target area being positionedwithin the vacuum chamber so that the plasma stream may be discharged bythe plasma generator and materials in the plasma stream may then bedeposited at the target area; (g) a means for injecting carriermaterials into the plasma stream; (h) an access door for the vacuumchamber, the access door permitting access to within the vacuum chamberfrom outside the vacuum chamber and the access door having sealingmeans, whereby said carrier materials combine with impurities in thesemiconductor materials when the carrier materials and semiconductormaterials are in the plasma stream and the materials are preferentiallyionized, thereby causing the impurities to separate from thesemiconductor materials while the materials are in the plasma stream.19. The apparatus of claim 18 further comprising a robot means, therobot means being operable to move materials to and from the targetarea.
 20. The apparatus of claim 18 wherein the semiconductor metal issilicon and the silicon is injected at the anode.
 21. The apparatus ofclaim 18 wherein the semiconductor metal is silicon and the silicon isinjected adjacent to the cathode.
 22. The apparatus according to claim18 wherein the vacuum pumping apparatus comprises a cryogenic vacuumpump and an ion vacuum pump.
 23. The apparatus of claim 18 wherein thesemiconductor materials supplied to the plasma generator aremetallurgical grade silicon, and the preferential ionization and theseparation of impurities from the semiconductor materials results insemiconductor grade silicon being deposited at the target area.
 24. Theapparatus of claims 18 or 23 wherein a coil assembly is provided forcondensing materials which escape from the plasma stream.
 25. Theapparatus of claims 18 or 23 wherein the plasma generator is surroundedby an accelerating magnet which accelerates the plasma thereby causingthe materials in the plasma to be transported away from the plasmagenerator.
 26. An apparatus for refining semiconductor metals used toform semiconductor junction devices by means of a plasma spraymagnetically accelerated in a vacuum comprising:(a) a vacuum chamber andassociated vacuum pumping apparatus; (b) a magnetoplasmadynamic plasmagenerator, the plasma generator further comprising:a cathode an anode anaccelerating magnet located adjacent that portion of the cathode closestto the anode a focusing magnet, at least part of which is located beyondthe anode with respect to the cathode; (c) a plasma generator supportstructure, the support structure supporting the plasma generator withinthe vacuum chamber; (d) a means to supply the plasma generator withelectric power, the electric power being primarily direct current andthe power enabling the plasma generator to create a plasma; (e) a targetsurface, the target surface being located beyond the focusing magnetwith respect to the cathode and anode; (f) a means for injectingmaterials into the plasma in order to create a plasma stream; (g) anaccess door enabling access to the inside of the access chamber from theoutside, the access door having a sealing means; (h) a coil assemblylocated substantially concentrically within said focusing magnet whichcools and thereby condenses gases escaping from said plasma; and (i) abaffle assembly located substantially concentrically within said coilassembly and surrounding said plasma so as to protect and separate saidcoil assembly from said plasma.
 27. An apparatus for refiningsemiconductor metals used to form semiconductor junction devices bymeans of a plasma spray magnetically accelerated in a vacuumcomprising:(a) a vacuum chamber and associated vacuum pumping apparatus;(b) a magnetoplasmadynamic plasma generator, the plasma generatorfurther comprising:a thermionic cathode an anode an accelerating magnetlocated adjacent the cathode a focusing magnet, at least part of whichis located beyond the anode with respect to the cathode; (c) a plasmagenerator support structure, the support structure supporting the plasmagenerator within the vacuum chamber; (d) a means to supply the plasmagenerator with electric power, the electric power being primarily directcurrent and the electric power enabling the plasma generator to create aplasma stream with ions from the thermionic cathode; (e) a target area,the target area being positioned within the vacuum chamber so that theplasma stream may be discharged by the plasma generator and thematerials in the plasma stream may then be deposited at the target area;(f) a means for injecting materials into the plasma stream; (g) anaccess door for the vacuum chamber, the access door permitting access towithin the vacuum chamber from outside the vacuum chamber and the accessdoor having sealing means; (h) a coil assembly located substantiallyconcentrically within said focusing magnet which cools and therebycondenses gases escaping from said plasma; and (i) a baffle assemblylocated substantially concentrically within said soil assembly andsurrounding said plasma so as to protect and separate said coil assemblyfrom said plasma.
 28. An apparatus for refining metals by means of aplasma spray magnetically accelerated in a vacuum comprising:(a) avacuum chamber; (b) a magnetoplasmadynamic Hall effect plasma generatorincluding:(i) a cathode, (ii) an anode, (iii) plasma accelerating meanslocated adjacent the cathode, (iv) plasma focusing means at leastpartially located beyond the anode with respect to the cathode, (v) saidplasma generator being supported within said vacuum chamber; (c) meanssupplying said plasma generator with electric power thereby enabling theplasma generator to create a plasma stream; (d) a target area positionedwithin said vacuum chamber for receipt of materials contained in theplasma stream; (e) means for injecting materials into the plasma stream;and (f) a coil assembly located in surrounding relation to said plasmastream which cools and thereby condenses gases escaping from saidplasma.
 29. The apparatus of claim 28, further wherein said cathodecomprises a thermionic cathode.
 30. The apparatus of claim 28, furtherwherein said plasma accelerating means comprises a magnet.
 31. Theapparatus of claim 28 or 30 wherein said plasma focusing means comprisesa magnet.
 32. The apparatus of claim 28 further wherein said electricpower comprises primarily direct current.
 33. The apparatus of claim 28or 32 further including an access door for the vacuum chamber, theaccess door permitting access to within the vacuum chamber from outsidethe vacuum chamber and including sealing means.
 34. The apparatus ofclaim 28 further including a baffle assembly located substantiallyconcentrically within said coil assembly and surrounding said plasmastream so as to protect and separate said coil assembly from said plasmastream.
 35. The apparatus of claims 28 or 34 wherein said coil assemblyis located substantially concentrically within said focusing means. 36.The apparatus of claim 35 further wherein said focusing means comprisesa magnet.
 37. The apparatus of claim 36 further wherein saidaccelerating means comprises a magnet.